1. Field of the Invention
The present invention relates to a window covering, more particularly to a window covering provided with a pull cord device.
2. Description of the Related Art
U.S. Pat. No. 7,406,995B2 discloses a pull cord device for controlling raising and lowering of a base rail of a window covering. The pull cord device includes a locking wheel having a toothed segment turnable between locked and unlocked positions to engage and disengage from a cord spool, respectively, a cord-release controlling member having a cord retaining region to engage a pull cord to be movable along a linear running path when the pull cord is pulled in the unlocked position, a guideway disposed in the locking wheel, and including an angularly extending first route and a looped route, a guided member having a key end disposed in the guideway, and a linkage coupling the controlling member with the locking wheel such that when the controlling member is moved, the locking wheel is turned from the locked position to the unlocked position, and such that, in the unlocked position, the cord retaining region remains unmoved in each of the regions in the looped route.
Although the pull cord device is capable of retaining releasably the base rail at a desired height, a braking effect of the pull cord device is not functional when the base rail is being lowered. Therefore, downward moving speed of the base rail may be too fast especially when the combined weight of the base rail and slats of the window covering is greater than the restoring force of a coil spring of the pull cord device, which can be a cause of injury to a person or damage to an object under the base rail.